This invention relates generally to a mechanical differential assembly and, more particularly, to a mechanical differential assembly having increased bearing load zone capacity.
Machines such as earth working machinery, paving machinery, load transfer carrying machinery and the like use differential assemblies in order to transfer power from a transmission to driving wheels. The differential assembly, in the most general form, consists of an arrangement of gears, bearings and a carrier provided within a rear axle casing of the machine. In operation, an output shaft of the transmission transmits an output torque to a bevel pinion gear of the differential assembly which, in turn, transmits the torque to driving wheel shafts for driving the machine.
More specifically, a typical differential assembly includes a bevel pinion gear which is coupled to the output shaft of the transmission. A pair of tapered roller bearings supports the bevel pinion gear. The tapered roller bearings permit the bevel pinion gear to freely rotate about the longitudinal axis of the output shaft of the transmission. The bevel pinion gear meshes with a bevel ring or crown gear that is coupled to a differential gear assembly. The differential gear assembly as well as the bevel pinion gear are housed within a carrier. The driving shafts of the driving wheels extend through a centrally located bore of the differential gear assembly. The differential gear assembly permits the driving wheels to rotate independently of each other such as when turning a corner or traversing an uneven road.
The differential gear assembly is supported by two opposing tapered roller bearings, each at opposing ends of the differential gear assembly. These tapered roller bearings permit rotation of the differential gear assembly, and are typically referred to as a bevel gear heel bearing and a bevel gear toe bearing. The toe bearing is typically smaller than the heel bearing. In order to function properly, it is critical that the tapered bearings be properly pre-loaded thus ensuring that the differential gear assembly is held in proper alignment and is free to rotate about the longitudinal axis of both of the driving shafts during the rotation of the differential gear assembly. The pre-loading of the tapered roller bearings also ensures that both of the tapered bearings are properly loaded during the operation of the machine. In this manner and with the proper pre-loading, the tapered bearings contribute to the performance of the differential gear assembly and hence the machine.
The pre-loading of the tapered bearings is of critical importance, where an improper pre-loading may result in a misalignment of the inner and outer races of either or both of the tapered roller bearings. Improper pre-load may also result in one or both of the tapered bearings operating with a diminished load zone, i.e., where only a few rollers of the tapered bearings carry the entire load imposed by the differential gear assembly during rotation thereof. This may then result in a potential roller overload thus causing a failure of one or both of the tapered roller bearings.
Pre-loading may be affected by many different environmental factors, all of which are important. First, pre-loading of the tapered bearings may be affected by a load placed on the machine, as well as the operating environment of the machine. Both of these conditions may result in a deflection of the carrier which houses the differential gear assembly. This deflection will then place a load on one or both of the tapered bearings thereby affecting the pre-loading, e.g., (i) negating the pre-load or (ii) adding further to the pre-load. In either situation, the pre-load will be influenced thus increasing the potential of failure of the bearings due to a diminished load zone.
A high torque output of the transmission output shaft also affects the loading of the tapered bearings. This is because an axial force will be placed on the differential gear assembly. In this case, the load on the heel bearing will increase and simultaneously unload the opposing toe bearing such that the toe bearing will operate with only a few of the rollers carrying the entire load of the differential gear assembly thus causing a bearing overload. This may result in a premature failure of either the heel or toe bearing. Another condition may simply be an improper pre-loading adjustment of the tapered bearings, or the tolerances of the casing or differential housing being improperly machined.
U.S. Pat. No. 3,175,417 to May, issued on Mar. 30, 1965, shows an axial carrier unit. In this unit, a differential gear assembly is positioned within a carrier and tapered roller bearings support the differential housing for rotation on opposing sides thereof. A bevel pinion gear meshes with a ring gear of the differential gear assembly. In this arrangement, the tapered bearings and more specifically the inner and outer races of the opposing tapered bearings are prone to misalignment due to deflections on the carrier and other loads placed thereon such as axial forces generated by the bevel pinion gear. This misalignment, in turn, results in a diminished load capacity of one or both of the tapered bearings and thus failure of the system.
The axial carrier unit disclosed in U.S. Pat. No. 3,175,417 also includes a stub shaft for connecting to a drive shaft via a coupling. The stub shaft is supported for rotation by a single roller bearing arrangement mounted at the forward end of the shaft and by a pair of tapered roller bearings mounted at the rear end of the shaft. These bearings do not carry the same loads as the tapered bearings which support the differential gear assembly, and thus the same considerations such as, for example, housing deflections which affect the loading of the tapered bearings supporting the differential gear assembly, are of no concern. Also, it is noted that the stub shaft has a different configuration than the differential gear assembly and thus has different loading, weight, torque and the like requirements.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.
In one aspect of the present invention a differential assembly has a differential gear assembly having a first end and a second end. A cylindrical bearing supports the first end of the differential gear assembly and a pair of tapered bearings support the second end of the differential gear assembly. Bearing cages retain the cylindrical bearing and the pair of tapered bearings on the carrier assembly.
In another aspect of the present invention, a differential assembly has a differential gear assembly and a ring gear mounted thereon. A cylindrical bearing supports the differential gear assembly at the first end and a first bearing cap retains the cylindrical bearing about the first end of the differential gear assembly. An inner and an outer tapered bearing support a second end of the differential gear assembly. A second bearing cap retains an adapter bearing cage which in turn receives the inner tapered bearing and the outer tapered bearing on the second end of the differential gear assembly.
In still another aspect of the present invention, a method of maintaining a load zone capacity in a differential assembly during driving conditions includes generating a thrust load on a differential gear assembly, transferring the thrust load to a pair of tapered roller bearings thereby eliminating axial forces on a cylindrical bearing.
In yet another aspect of the present invention a machine having a rear axle is coupled to a differential assembly. The machine includes a rear axle housing having a bore and a differential gear assembly having a first end and a second end mounted within the bore. A cylindrical bearing supports the first end of the differential gear assembly and a pair of tapered bearings support the second end of the differential gear assembly. A first bearing cap retains the cylindrical bearing about the first end of the differential gear assembly and a second bearing cap supports a adapter bearing cage which in turn supports an inner and outer tapered bearing at the second end of the differential gear assembly.